Relay system and associated circuits therefor



Nov. 16, 1943.

H. E. GOLDSTINE RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June5, 1940 6 Sheets-Sheet l (Ittorneg Nov. 16, 1943. H. E. GOLDSTINE RELAYSYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6 Sheets-Sheet2 ll 55% \WGERMQ EEGQS 010114115 aazdsifiii i attorneg m I Mm wstibwswwhs Nov. 16, 1943.

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RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June 5, 1940 6Sheets-Sheet 5 7'0 0/) SYSTEM 70 flurammc FBEOI/EIC) comma 00/7 3nnentorflaZknE Gamma Nov. 16, 1943.

H. E. GOLDSTINE RELAY SYSTEM AND ASSOCIATED CIRCUIT THEREFOR Filed June5, 1940 e Sheets-Sheet e 3nvze n tor (Ittorneg flazzmzt G5 w)? PatentedNov. 16, 1943 UNITED ,1 PATENT 7 lassifies RELAY SYSTEM AND Assoonirsnamounts THEREFOR I HallanE Goltistine;Tort Jeifer'son, N}: assign z [orto Radio Co'ffiii'ration of Am rica',a corpora- .7 non etnelawareAiimieatitn June 5. 1940, Serial Noi eaasea f This invention relatesgenerally to laying system. More'partielilally, the inven= tion relatesto such features as 1) the frequency modulator circuit, (2) therepeater'station for receiving a frequency modulated signal on onecarrier'i'reqlienoy and relaying or retransmitting this frequencymodulator signal. on another -car'-'- rier frequency, and (3) theantitcainatic frequency control circuit employing cavity or concentricline resonators.

The following is adetailed diseussion 0f the invention accompanied bydrawings, wherein Fig. 1 shows very generally a eofnplete radioi relaysystem in which the present; invention may beemployed; Fig. 2 shows.the'ireiiuency modulatorsystem oi the inventioneiiiployed in a repeaterstation of the system; of f Fig. 1 --fOr converting video signals intofrequencymodulated high irequeneey signals; Figs. 3a-and Blitakehtogether show apparatus employed atone of the repeater Patent"2}239,724,' granted April 29; 1941.

aeeemmodate the full band snectrum of high definition television. This;antenna consists of two separate and independent radiator systems, I and2; the former fersound andthe latterfor vision transmission, bothradiators being sum ported on a eofnmongcelumh located an appre= ciabledistance aboveg-rounmhsually on the top of-awtall building 1 Thewantenhasystem of the transmitter Stati'on Ais of thez'type' installed at thetop of the Empire State Building in New York; New York; aridisdescribedquite adequately in the opend ing "apDIiEQtiOr-I 0f N118 E;Lsihdenblamiserial N0.

2081573-fl1d May-..18, 1938;"1'1OW United States The antennas onstatlonsB, G and D are of the uni directional type, there :helng usedapairofah or relay stations of the system of Fig. '1' for.

ignals of the orderoi si x' inet rs andless; and may he" used forthe'transmission of television signals; although it will be underst odthat it may also beus'd totrahsmit' telegraph si nals or any etherty'peof radio signal. The system includes a transmitting station 'A',lurality or intermediate re eater or relaystations .3 amp, and areceiving station D, suitably spacedaflart along the line oftransmission. litepeater station's B and C are designed terepeat thesignals from station A to station D. The-arrows indicate the directionsof the sighals'between the =respe'c tive stations. Although onlytworepeater stations have been shown, it shouldiloe understood:

that this nuinheris illustrative of any number of repeater stationswhiehmay be located atq frequent intervals along the line "of transmis-ision, for relaying and amplifying signals.

The antenna system indicated at the transmitting station A of Fig.-;1-is shown to beer the voiimidirectional--tyfie, havifig constantcharacter istics over a frequency bane sufiieieiitiv wiaeto tennas at'fihe% intermediate istatibnsB and C, one forireeeivirig thewsignalsifrom:the nearest transmittingiantenha'anti the other for repeat= vingandifieradiating tlie signals to the neiit. re-

pater-orirelaystation along "the line of trans= mission; Sineewthetransmission range 'of the ultra short waves at which this system isdesigned i rte junction deiienels' substantially upon the airsl-ifie, orvisual distance; a factor propore.

tio'nal to the lieight above the. earths surface, it isproposedttoiloeate all stations at points having asg'featrlieightwas'possible; such asflon moun tair'isj tall huildings,radio .iinasts,, tc. The re= ,eeivingi antennafifi at repeaterwstation Bconsists of :afiair of" dipole. arrays placed. one behind theJUthrliands'hitably phasd relative to' each otherifieeiprovidingaaunidirectional efieot. This 1 antenna isdsigned to receive the signalstransmittedfriiinstation-YA. Referene is hereby made to Garter, UnitedStates Patent No. 2,-183,784;"granted Deeei'nbertw; 193.9,ior a shitibledeshrihtibmbf antenna 1 The reradiating i or transmitting antenna!or station B is of the rhetal parahohe'typewhich has at its focus adipole or at plurality or dipole antennas arranged in mesa-me straightline; These dipole antennas niaya be oi the folded type which has. beenfound to he more-leffeetive than thesingleidifidleand is oreierably ofthe general-form described in the eoperitiing implication" of Philips;Carter Serial Ila-"155,385, filed J uly 24, 1937', he? United statesPatent 2383,9145; gr83nted-=May 2l5,' 19 12. At "re:- peater station Cthererar'e shown a r'eceivingam tenna '5, "andia reradiatingUr-transmit-ti-ng an- 1 teiina; Gybothof the parabolic type employingfolded dipole sahtenhas "as'described in :ECjIlflBC-Y tion withantennafl of station B. 'Antenr'iais'ii anti 6: are,of course effectivein difierent direc tions, the receiving antenna being positioned (.toreceive the signals from station B while the tower. The antenna 1 atreceiving-station D comprises a parabolic -reflector having at its focusone or more dipoles, preferably folded up dipoles, l0

' this antenna being, of course, directed to receive the signals fromantenna 6 of the adjacent repeater station. The antennas of stations.A'to D, inclusive, have been described as being of particular types,mainly by way of example, since it is apparent that other types ofantennas can be used to achieve the desired results.

In the operation of the system'of Fig. 1, television signals emanatingfrom broadcasting station A are amplitude modulated and radiated atafrequency of 45.25 megacycles and received on an antenna 3 at stationB,from which the signals pass to a television receiver thereat-to provideavideo component, theband width of which may besubstantially of the orderof 4 megacycles The video output of this television receiver at stationBisrused to control a trans mitter with multi stages of frequencytripling,

described more in detail later in connection with Fig. 2. The output ofstation B radiated from antenna 4"is'a frequencymodulated wave of theorder of 500 megacycles; (in one particular embodiment tried out. inpractice the output was about474 megacycles'witha band frequencydeviation of plusand minus about 3.5 megacycles).

\ At repeater station Cthe receiving antennai receives the 500.megacycle afrequency. modulated signal. radiated by. antenna 4 of.station B, and

x converts the signal bymeansof apparatus described later in more detail;in connection-with 40 Figs. 3a and 3b to a 100zmegacycle signal formore efficient amplification. This 100.megacycle, signal is thenamplified and converted to an output-frequency. modulated signal havinga'mean frequency. different than'the incoming frequency, 4;")

' let us sayafrequency of'.512.6 megacycleawhich is thentransmittedbyantennafi towardthe next. adjacent station, in this case receiver.sta-, tion D. At theifinal receiving station;.,-D in the radio link,vtherfrequency modulated signal 59 of 512.5 megaoyclesis received onantenna 7. and converted to a lower frequency 'signalwhich is thenamplifiedand amplitude'limited before it is passedlon to a detectorwhich transforms the frequency modulated signals to amplitude modu- 5.5latedzsignals. From the foregoing, itv will be seen that the amplitudemodulated signal transmitted by the T broadcasting transmitter atstation A at one frequency is received at station B and converted to a'frequency modulatedsignal 60 of a different frequency which is thenradiated todstation C wherethis frequencymodulated signal ischanged to afrequency modulated signal having-another and different carrierfrequency,- after whichthe last converted signal is .trans- 35 mitted tostation .13 where it may be converted to-an amplitude 'modulated signalforlocal use or for use in affecting another broadcasting station tosend out. the television signals over one or more additional stations.

' Fig. 2 illustrates the frequency modulated cir-" cuit .employed atstation B for producing a desired frequency modulated. signal from the:am-

'plitude modulated waves received'at this station. The'system of'Fig. 2.comprises a master; 75,

oscillator 8, a frequency modulator circuit 9, a

first tripler stage II] for tripling the frequency impressed thereon, anamplifier stage II for amplifying the output of the first tripler stage,and a second tripler stage [2 for tripling the frequency in the outputof amplifier ll,'alsoa final amplifier stage l3 of the inductive outputelectron discharge'device type, and an automatic frequency controlcircuit I4 for stabilizing the frequency of the master oscillator 8.Although stages 9, l0, II and I2 are each shown as comprisinga pair ofelectron discharge devices arranged in push-pull, it should beunderstood that if desired the two vacuum tube electrode structures ofeach of these stages may be included withina single evacuated envelope.As an illustration, the push-pull electrode structures of stages 9 andI0 may each be constituted bya single electron discharge device tube ofthe RCA 832 type, while the amplifier stage II may be I constituted by asingle electron discharge deviceof the RCA 829 type. The second triplerstage l2 may be constructed in accordance with the teaching described inthe copending ap-, plication of Orville E. Dow; (Serial No. 302,655,

filed November 3, 1939, now United States Pat.-

ent 2,253,849, granted Aug. 26, 1941, while the amplifier stage I3 maybe of the type described in the copending application of Fred H. Kroger,Serial No. 296,045, filed September 22, 1939. In the operation of thecircuit of Fig. 2,'the video component of .the signal received atstationB is applied in parallel to the two control grids of the.electrode structures of the frequencyv modulator-9, which functions tomodulate the output of the master oscillator 8.. The master oscillatonasan example, may. generate oscillations of a frequency of the order of,52.67 megacycles. The. output from the master oscillator is passed ontothe frequencymodulator stage 9 and the frequency modulated waves thenimpressed upon the jfiISt tripler stage III, which provides an out- 7put of,'let us'say, .158'megacycles, this last outputbeing amplifiedinstage II and then passed on to the second tripler stage I2 from whichthere is. obtained, let us say, an output of 4'74 megacycles with a bandfrequency deviationof approximately plus and minus four megacycles,

which .last output is passed on to the amplifier stage l3 from whichenergy isderived for radiation by the antenna 4. It should be noted thatthe frequency modulator is capacity coupled to.

the master oscillator 8 by means of condensers C1 and C2, although itshould be understoodthat, if desired, inductive coupling may be employedby the'useof suitable transformers between the master oscillator and thefrequency modulator.

The condenser C3 in the frequency modulatorv stage 9 is of very smallvalue compared to the to .the

modulation but fairly large compared radio frequency. v

The amplifier stage-J3 consists of an electron discharge device circuitcomprising a vacuum tube structure, generally of the, so-calledinductive output type consisting of an evacuated glass envelope. Econtaining'within it anfindirectly heated cathode K, a filamentor'heater F, a gridv G, ringlike accelerator electrodes M,- M, acollector electrode R, and a suppressors. The heater 1 may be suppliedwith energy from a suitable alternating current source ihrough chokecoils (not' shown) Connected tothe grid Gis a connection extendingto-the outputof the tripler stage I2.

The collector electrodeR forgathering the elec- 2 trons traversing thelength of the glass envelope supply 2B.

E is shown to be cup-shaped in formalthough', if desired, it may behemispherical, conical or of other'suitab-le shape." Centrally locatedwithin the interior of collector R'there is'provided a rod-likesuppressor electrode S for gathering secondary electrons which mayemanate from',R. The suppressor S may take any suitable formaccording tothe design of "the'collector R. Accelerator electrodes M, M are narrow'in-width and are maintained 'at a suitable positive potential relativeto the cathode. Surrounding the-exterior of the glass envelope E andlocated intermediate the two accelerator electrodes M, M there is provided a tank circuit [5 (hour-glasstype) in the form of a surface ofrevolution gwhose central surface is perpendicular tothe electron beamemanating from-cathode K. This tank circuit is symmetrically arrangedaround the glass envelope E and is provided with a gapa, b.Theconfiguration of this tank circuit l5, as-shown in the drawings, isthe cross section of a surface of revolution through the axis ofrevolution in the plane of the drawings and approximates two equalsectors'with their vertices toward the glass envelope E. The dimensionof the tank circuit I5, as measured from the center of the glassenvelope to the arc of the sector, is approximately one-quarterof thelength of the communication wave corresponding to the resonantfrequency, provided that the gap at, h is not supplied with capacitordiscs to change the frequency to a value less than the natural frequencyof the resonator. This tank circuit is a high Q, low loss circuit and ispreferably made of a high electrically conducting material such ascopper. For focusing the electron beam there are provided a plurality ofmagnetic lenses (not shown) in series relation and surrounding the glassenvelope, the magneticfield being provided by a strap of iron I6 whichis placed adjacent the sides of one .of the sectors of the tank [5andthen completed through an iron core H, in turn 'surrounded by anelectromagnetic field .coiforsol'enoid l8 excited byv adirectzcurrentsource. of A suitable output coupling coil 2| derivesenergy from the tank circuitand supplies this energy to the dipoleantenna 22 ofithe antcnna system 4. Themanner in which the amplifiercircuit l3 functions isnow well understood and is described quiteadequately in. the Kroger copending application Serial No. 296,045,supra, to which reference is herein made.

In order to stabilize the frequency of the mas-'- ter oscillator 8,there is provided an automatic frequency control .(AFC) circuit I Iwhich iscoupied between the master oscillatorB and the out put of thesecond tripler stage 12. AFC circuit it comprises a pair ofrectifientubes 23 and 24 supplied with radio frequency energy from thetuned circuits 25 and 26, .the latter in turn being coupled to thetripler stage l2 by means oftconnection 21. The tuned circuits 25 andhave intersecting resonance curvesat the mean or assigned carriedfrequency of the output of the sec;

ond tripler, stage [2, with maxima at frequencies lying either sideofthe, output'frequency of the tripler l2, these, tuned circuitsapplying the potential fluctuations to the anodes of the two detectortubes 23 and 24 so that output current balanced amplifier circuitcomprising vacuum tubes 28 and 29in whose anodeicircuits is connected apolar relay 3ll, the latter in turn controlling the directlon ofrotation of the reversible motor 3| whose shaft 32'is shown in dottedlines connected tothe condenser 33for controllingthe frequency of (themaster oscillator 8. It'should benoted that the outputs of tubes 28 and29 are in opposition to each other and it will thus be obvious that withequal current. flow through both tubes28 and 29 the polar relay 30 willhave its armature in mid position, without causing the motor to rotateoneway or the other. Any fre quency change in the output of the triplerI2, produced let us say by the change in the frequency of the masteroscillator 8, will cause one of the two resonant circuits 25, 26 tobecome more strongly energized than the other, as a consequence of whichthere will be a greater fiow of current through one of the tubes 28 or29, depending upon which cf the tubes23 and: 24 is more strongly excitedwith departure of frequency from the assigned carrier frequency. The netresponse in the polar relay 30 will-beproportional to the differencebetween the assigned carrier wave in the output of the tripler stage 12and the wave impressed by the tripler l2 upon the tuned circuits 25 and2B. A departure from the desired mid band frequency will thus unbalancethe direct current voltages in ,the outputs of tubes 28 and 29, and willcause thepolar relay 3!) to affect the motor 3| to rotate in onedirection or the other, depending upon whether the frequency is higheror lower than the desired mid band frequency in the output of thetripler stage. The rotation of the motor 3| will be in such direction asto cause *the condenser 33 tochange its value such that the masteroscillator 8 returnsto .a frequency where the signal in the output ofthe secondtripler I2 is again at mid band assigned frequency. l V

- Figs. 3a and 3b considered together, illustrate the apparatus at therepeater station C of Fig. 1, and includes a receiving antenna 5, areceiver 34 for converting the received incoming signal which is of theorderof 500 megacycles to an intermediate frequency of megacycles, afrequency converter inductive output electron discharge device 35, anamplifier 36' also of the inductive output electron discharge devicetype, a local oscillator circuit consisting very generally of a masteroscillator 31, a first frequency tripler stage 38, an amplifier stage39, a second frequency tripler stage 40, and an amplifierof 'theinductive output electron discharge .device type 4!. There is' alsoprovided an automatic frequency control (AFC) circuit 42 for stabilizingthe frequency of the master oscillator 31; The

receiver 34, which is shown. conventionally in box form, includes anultra high frequency converter unit for converting the incoming signalwaves of the order of 500 megacycles to anintter mediate frequency ofabout 100 megacycles, and also intermediate frequency amplifierapparatusfor this 100 megacycle band. The ultra high frequency converter unit ofthe receiver 34 is shown in Fig. 4, which will be. described later. Theautomatic frequency control circuit 42 is shown in more detail in Fig.5, which isalso to be described in greater detail later.

In the'operation of Figs. 3a and 3b, the in coming signals received onantenna 5 are converted to an intermediate frequency of about 100megacycles by the receiver of Fig. 4 and passed on to the output circuit43 which is designed-to pass a wide band of frequencies on both sides ofthe mid band intermediate. frequency. Output circuit 43 is shown coupledthrough a concentric line connectingfcircuit 44 to the grid of theinductive output vacuum tubeiconverter 35 to whose cathode circuit thereis inductively coupled the amplified output of th local oscillator.Converter tube 35 is generally of the type described above in connectionwith the amplifier I3 of Fig. 2, and a more detailed description thereofis to be found in the copencling Kroger application, supra. The cathodecircuitfor the converter tube 35 includes a coaxial line 45, the innerconductor of which is coupled to one leg of the heater while the outerconductor is coupled to the other leg of the heater. By means movablealong the jlength of the coaxial line 41 to the mid frequency of theband pass.

of the arrangement shown, the cathode circuit 3 comprises, in effect, aparallel tuned circuit tuned to the 412 megacycle frequency and towhichis coupled the loop extending-to the output of the inductive outputvacuum tube 4| of the local oscillator circuit. Since the amplifier 4|is designed to amplify oscillations of the order of 412.5 megacycles,.in the manner described in more detail hereinafter, the converterfunctions to provide in its output circuit a mid band frequency of theorder of 512.5 megacycles; which is then passed on throu h a coaxialline affair 41 to an inductive output type of amplifier 36 Where thesignal having a mid band frequency of 512.5 megacycles is amplified andthen passed on to the antenna system 6 for radiation to the nextadjacent station.

It should be notedthat energy is derived from the output of theconverter circuit by inductive coupling tothe coaxial line 4'! over ametallic strip 48 which extends within the tank circuit of the convertertube 35 but is insulated therefrom. The outer conductor of the coaxialline line 41 is grounded, insulated from th tank circuit of converter35, and has its ends adjacent this tank circuit provided withflange-like metallic strips -49- which extendon opposite sides of theaperture in the tank circuit. 'It should be noted thatthe tank circuitis here maintained at a positive potential relative to ground and thatone or more accelerator. electrodes of the electron discharge deviceiscoupled 'to the tank circuit through a resistor. This arrangement ismerelyfor simplicity of design, since it will-be obvious that if desiredthe ring-like accelerator electrodes can be provided with a positivepotential while the tank circuit is left free or grounded.

In view ofthe fact that the outer conductor of the coaxial line 41 isgrounded, and the tank: circuit maintained at a positive potential, itis necessary to isolate the inner and outer conductors of the coaxialline 41 from' the tankcircuit and this is done in themanner shown in thedrawing by means of the .fiange 48 and 49." The aux+ iliary pot orcoaxial line 50 is, in effect, a tunable inductance arrangement which;tunes the output circuit for the converter and is provided with aslidableconnection 5| movable. along the inner and outer conductorsofthe coaxial line 50 for adjusting the inductance of the circuit.-. .Ineffect, that portion of the tank circuit of: the converter which islabeled 52 constitutes'a loop made up of a metallic flange 53 andconnected at one end to the arc of the tank. The tank-circuit comprisesthe primary of a transformer, whose secondary circuit consists of theloop 52,. the flange 48, the coaxial line 41 and the coaxial line tuninginductance 5U. The coaxial line 5|] then servesto tune the secondarysince it .is

ductor of. the line '41. The coarse tuning-of the v output circuit ofthe converter is first effected by moving the position of the coaxialline inductance 50 suchthatthe secondary circuitis tuned The variablecondenser 54 serves as a micrometer adjustment to tune the secondary.The area of theloop 52,- of course, must be adjusted to first obtain thedesiredband pass and then for uniform response in the band pass theoutput circuit of the converter is adjusted by means of the slider 5|while maintaining constant the position of the line50. One advantage ofthe particular output arrangement just described is that the feed lineto the next adjacent stage is mainmained fixed at all times and need notbe moved. In this connection, attention isinvited to copendingapplication Serial No. 346,106, filed July 18, 1940,.jointly by myselfand Orville E. Dow, for a description of a similar coupling circuit.

The amplifier 36 is energized from the coaxial line 41. over the loop 55which is inductively coupled to the loop 56 comprising suitableconnections. between the grid and the cathode of this amplifier stage.Here again it will be noted that the tank of the amplifier 36 is shownmain! tained at a positive potential while the output circuitfor theamplifier 36 is substantially similar to the output, circuit for theconverter 35, and possesses thesame relative advantages. The grid of theamplifier 35 as well as the grid of the converter tube 35 are maintainedat suitable negative values relative to the cathode.

Stages 31, 38, 39 and14|l of the local oscillator circuit are similar inarrangement to stages 8, III, II and |2, respectively, of Fig. 2, andare designated in the same manner. The master oscillator 31 is designedto generate oscillations of the order of 45.83 megacycles, theseoscillations in turn being-tripled in frequency by the stage 38 to 137.5megacycles. then amplified in stage 39 and the frequency again tripledby stage 40 to 412.5 megacycles, this last frequency being impressedupon the grid of the inductive output amplifier 4| and the amplifiedoscillations derived therefrom by loop 51 applied .over line. 58. andcoupling loop 46 to the tuned cathode circuit of the converter tube 35,wherethe oscillations from the local oscillator are. beat with theintermediate frequency of megacycles to provide a sum frequency, thelatter being passed on from the converter to the amplifier 36 in themanner described hereinabove.

Amplifier 4| is-alsoof the type previously de-, I

scribed above in connectionwith the'amplifier l3 of Fig. 2, and isdescribed in greater detailin the ,copending Kroger application, supra.

From the foregoing, it will'be seen that an'incoming-frequency modulatedsignal of one carrier frequency is received by the repeater station ofFigs. 3a and3band changed at this station to a frequency modulatedsignal of another carrier frequency. The incoming received frequency isfirst changed from the order of 500 megacycles to l00r-megacycles formost efficient amplification and thenthe frequency of 100 megacyclecomponent' increased to a different frequency, for example 512.5megacycles, which is thenradiated.

.The ultra high frequency converter unit employed in the receiver 34 ofFig. 3a for changing the incoming frequency of the order of 500 mega-The output of stage 38 is figure illustratesia system very tgenerally'ofthe type described in copending application 8erial No. 222,104, filedJuly 30, 1938, by KG. McLean, now United States-Patent 2,236,004.,granted March 25, 19,41, Vand, if desired, may comprise thev identicalconverter unit arrangement shown in this copending applicatiomiReferring to'Fig.:4 in more detail, there is shown, conventionally, a":detector III) to whose grid is fed the incoming signal energy arrivingfrom the antenna and to whose cathode is supplied oscillatory energy:-irom a local high frequency oscillator I22. Both the detector IIIIandthe oscillator [22? have, re spectively associated therewith,concentric line. resonator circuits I III, I02, each having an outerconductor andan inner conductor. The inner conductor of resonator lfllcarries a multi-fingered contact section Hi4 which provides contact tomovable piston [05 on which is mounted the tuning capacitor plate I05.The concentric line I 02 has for its: inner conductor a pair of tubularconductors H6 and I placed end to.v end and coaxially arranged withrespect to the outer conductor. The tubular conductors H4 and U8 havetheir adjacent ends spaced. apart andprovided with capacity plates I23which are adiust-- able with respect to one another for tuning purposes.The tubular conductor H4 is also provided with a multi-fingered contactsection as shown, and a movable piston. on whichis mounted one of thecapacitor plates 103. The: output I09 of the detector 0 receivesthe'beat irequency (100 megacycles) of the incoming signal wave andthe-local oscillator frequency and extends to an intermediate frequencyamplifier circuit, not shown. The intermediate frequency coil I08 istuned by a copper slug. which is adiustable in position inside the coiliorm. An inspection of the detector unit H0 will show that there isincluded in each-leg of the filament or heater thereof a filter :unitcomprising choke coils I26 and low pass ifilter condensers t2t.v Thefilament and the anode circuit of oscillator I22 are also similarlyprovided with filter elements I25 and I 21, generally of the same typeshown in connection with the detector unit. The filter elements of thedetector unit I I0 and the oscillator unit I22 are divided into shieldedcompartments and the vacuum tubes per so are also shielded both from theshielded elements and the filter units and from the associatedconcentric line tuned circuits. The cathode of the detector H0 isconnected to the oscillator concentric line through a bias resistor andcondenser combina* tion I I3 and H2. The. oscillator I 22,- it shouldbeobserved, comprises a vacuum tube whose anode is grounded "to the shieldor outer conductor-of the concentric. line through a'by-pass condenserI2 I and-whose gridelectrcde is coupled through a coupling condenser II!to the plate. Hi3 ofz the lit)? the usual pair; of; rectifier or diodetubes coupled to'ofi tuned circuits whose resonant characteristicsintersect at the assigned mid band intermediate frequencya When metalvane II-Iv is rotated in response to an unbalance in the discriminatorcircu-it caused by the departure of frequencyfrom the desired frequency,such that the vane is parallel with the. axis of the inner conductorsI16 and H4, it-will be seenthat con-,

siderable flux aboutthe tube I'M-is interrupted, and the inductance of,H4 is reduced, thus raising the oscillator frequemzy. One the'otherhand, whengvane H1 is. rotated 90 from this position relatively littleflux is interrupted and the frequency lowered Afriction clutch ispreferably used between the motor 134 and the vane [[1, .so that thevane may be set at the centerzof its tuning range by a. suitable panelcontrol knob, thelatter also serving to indicate the position or thevane. I

Fig. 5 illustrates the preferred form of automatic frequency controlcircuit designated by box. 42in Fig, 3b, and comprises a pair of Vacuumtube detectors-V I and 1,51' associated respectively with concentricline resonator circuits 152 and [53. Resonatorcircuits [52. and IE5 haveintersecting resonance, curves with maxima at irequencies lying eitherside of the assigned operating frequency of 51125 megacycles in theoutputof the amplifier 3 6 of Fig. 3a. Energy from. the output of theamplifier 36 of Fig. 3a. is fed through transmission. line TL which iscapacitiveIy coupled to bothconcentric line resonators. I52 and I53,andtthe rectified outputs on the, cathodes of the rectifier'tubes [50and tilt are applied in push-pull to the balanced vacuum tube amplifiers[54' and [5.5. Theanodes of both amplifier tubes are connected throughleads I756 to the opposite terminals of. the windingof sensiti'vepolar'relay [51. Tubes l54 and I55 areprovi'd'ed with screen gridssupplied with a, positive potential through .a voltage regulator tube158, and with suppressor grids which are connected to their cathodes, asshown. A reversibletmotor inner conductor N6 of the associatedconcentric line resonator 102, the latter tunc'tioning as a frequencycontrolling element; A resistor H8 connects the grid oftheoscill'atortoground, I

In order to. compensate rordriitmg either of the oscillator I22 of Fig.4 or the"v signal freiquency received over the antennaxi, there. ispm'evided an. automatic tuning device comprising: a. reversible telechronmotor I34 which drives. a metal vane H'I located below the inner,conductor Ilfiof the; concentric line I02. Controitvoltage for theautomatic frequency control motor-13.41 is obtained from a discriminatorcircuit in. the:

I59 controlled by polar relay I51 functions to vary the position of thecondenser in the master oscillator circuit. over a flexible shaft [60.In view of the sensitivc nature of polar relay [51 there are providedtwo ruggedauxiliary motor relays LEI" and I62 between the motor- 159 andthe polar relay. I51 in orderto protect this polar relay. Thecircuitvfor operating the motor either in one direction or the otherwill be obvious from a mere inspectionjof the contact arrangement shownin the drawings, it

being understood, of course, that the polar relay I51 will moveitsarmature one way or the other depending'upon whether amplifier tubel54or;

I draws more current than the other. Normally, when thereis no driftfrom the assigned mid band frequency, the outputs of both amplifiersl5land I55 will be the same and balanced; as a consequence-of which thepolar relay I51 will be in the position shown in the drawing with thearmature midway between its opposed contacts. Whenever a drift in the.frequency occurs, the-rectifiers I50 and [5| will draw difierentcurrents and influence their respective amplifier tubes I55: andv I54,respectively, to operate the polar'relay I51 such that the motor I59will rotate itsshaft 1-60 to vary the tuning of master oscillator in amanner torestore the frequency to the desired value.

output of the ultra high frequency converter unit.Thisoiscri-minatorcircuit may' comprise at the termination thereofnearest said resonator circuits for matching the impedance of saidfeeder, and means for tuning out the capacity across said resistor.

5. In a radio system, means for producing energy which is frequencymodulated including an oscillator, an automatic frequency control cir-,-cuit for said oscillator comprising two concentric line resonatorcircuits having intersecting resonance curves with maxima lying eitherside of the mean operating frequency, a coaxial line feeder having itsinner conductor capacitively coupled to the inner conductors of said tworesonator circuits in electrically parallel relation for supplying saidtwo resonator circuits with said frequency modulated energy, means forconnecting the outer conductors of concentric line resonator circuitsand said coaxial line together and to ground, a resistor connectedbetween ground and the termination of said feeder nearest said resonatorcircuits, and a variable inductance element in parallel to said resistorfor turning out the capacity across said resistor.-

6. A system in accordance with claim 5, characterized in this that saidvariable inductance element is a coaxial line, the inner conductor ofwhich is connected at one end to that ter minal of the resistor which isconnected to said feeder, the other end of said last inner conductorbeing directly connected to the outer conductor.

7. In combination, an oscillator having a frequency controlling element,a frequency stabilizing circuit comprising two concentric lineresonators having intersecting resonance curves with maxima lying eitherside of the mean operating frequency, means for supplying frequencymodulated energy of said mean operating 'frequency to said tworesonators in cophasal relation, a rectifier connected to each resonatorfor obtaining a direct current component therefrom, a first relay, abalanced amplifier circuit coupled to said rectifiers and responsive toan unbalance in the outputs of saidrectifiers to operate said relay, apair of contacts on said relay, second and third relays connected tosaid contacts and alternatively operable in response to the closures ofsaid contacts, a reversible motor connected to said second and thirdrelays and responsive tothe operation thereof for varying said frequencycontrolling element in a direction to lessen said unbalance.

8. A frequency stabilizing system comprising two resonator circuitshaving intersecting resonance curves with maxima lying either side ofthe mean operating frequency, a-

feeder for supplying said two resonator circuits cophasally with saidfrequency modulated ener y, rectifiers for said two resonator circuits,the

outputs of said rectifiers being coupled to a circuit responsive to thedifference voltage, a resistor-connected to said feeder at the terminameans for turning out the capacity across said resistor.

1 9. A frequency stabilizing system comprising two resonator circuitshaving intersecting resonance curves with maxima lying either side ofthe mean operating frequency, a feeder for supplying said two resonatorcircuits cophasally with said frequency modulated energy, rectifiers forsaid two resonator circuits, the outputs of said rectifiers beingcoupled to a circuit responsive to the difference voltage, a resistorconnected to said feeder at the termination thereof nearest saidresonator circuits for matching the impedance of said feeder, and avariable inductance element in parallel to said resistor for tuning outthe capacity thereacross.

10. A frequency stabilizing system comprising two resonator circuitshaving intersecting resonance curves with maxima lying either side ofthe mean operating frequency, a feeder for supplying said two resonatorcircuits cophasally with said frequency modulated energy, rectifiers forsaid two resonator circuits, the outputs of said rectifiers beingcoupled to a circuit responsive to the difference voltage, and aresistor connected to said feeder at the termination thereof nearestsaid resonator circuits for matching the impedance of said feeder.

11. In combination, an oscillator having a frequency controllingelement, a frequency stabilizing circuit comprising a pair of resonatorshaving intersecting resonance curves with maxima lying either side ofthe mean operating frequency, means for supplying frequency modulatedenergy of said mean operating frequency to said two resonators incophasal relation, a

rectifier connected to each resonator for obtaining a, direct currentcomponent therefrom, a

first relay, a balanced amplifier circuit coupled to said rectifiers andresponsive to an unbalance in the outputs of said rectifiers to operatesaid relay, a pair of contacts on said relay, second and third relaysconnected to said contacts and alternatively operable in response to theclosures of said contacts, a reversible motor connected to said secondand third relays and responsive to the operation thereof for varyingsaid frequency controlling element in a direction to lessen saidunbalance.

HALLAN E. GOLDSTINE.

